1. Field of the Invention
The present invention relates generally to packing structures for chemical process equipment and, more particularly, to packing elements for use in randomly packed beds of mass transfer towers and in randomly packed beds for use in heat sink applications.
2. The State of the Prior Art
It is conventional to provide a mass transfer tower for use in transferring one or more components from one immiscible phase to another. Where the component is a chemical, it may be a gas component to be removed from a gas stream by absorption, or a component of a liquid mixture to be treated by a distillation or separation process. For such applications and a plurality of other applications involving mass transfer, it is conventional to pass the fluid to be treated through a column containing beds of randomly disposed packing elements. These elements are hereinafter referred to as packing elements.
It is known that the most efficient packing elements are those that present the largest surface area for contact by the fluids undergoing mass transfer. There have therefore been many attempts to design random packing elements with a maximum percentage of surface area. However, other characteristics are also desired. For example, it is important that the elements do not nest too closely together when in the randomly packed beds as this reduces the effective amount of surface area available for exposure to the fluid streams. It is also important that the elements do not pack so tightly together as to restrict the fluid flow, thus causing an increase in the pressure drop across the bed. Another concern, especially in the design and manufacture of ceramic elements, is that the maximization of surface area and the provision of proper drainage often comes at the cost of mechanical strength of the element. If the element fractures during installation or use in a bed, nesting may result.
Such packing elements, if constructed from suitable materials having appropriate heat absorption and retention characteristics, may also be useful in heat sink applications.
The present invention provides an improved packing element typically used in the chemical process industry in various operations where a gas stream is brought into contact with a liquid stream. Multiple packing elements are installed into a process vessel to create a packed bed. The unique shape of the packing elements of the invention was developed to provide minimum pressure drop across a packed bed while maximizing the available surface area for contacting liquid and gas streams. In accordance with the invention, the improved packing elements may also be used in connection with heat sink applications. Thus, a vessel, such as a column, chamber or tower, may be packed with a bed of the elements which is used to capture and retain heat from a first fluid medium and subsequently release the heat to a second fluid medium. As will be appreciated by those skilled in the art, the respective media may be a gas or a liquid. In particular, the elements of the invention may be used as a packing for a heat sink utilized in connection with a regenerative thermal oxidizer. Hot exhaust gases from the oxidizer is passed through a bed packed with the elements of the invention and the heat is transferred to the elements. Thereafter, a valve is switched and a relatively cooler fluid is caused to flow through the packed bed to pick up heat from the elements. The fluid heated in this manner may be an inlet fluid to be introduced into the oxidizer. In such application, only a single fluid traverses the packed bed at any given time; however, both surface area and low pressure drop remain important. It is to be noted in connection with the foregoing that heat sinks are well known applications which may also be used in a variety of industrial operations other than regenerative thermal oxidation.
In accordance with the concepts and principles of the invention, an improved packing element is provided for use in a mass transfer tower. Alternatively, the packing element of the invention may be use in heat sink applications as discussed above. The packing element comprises a saddle shaped member having a configuration generally corresponding to a portion of a toroid generated by rotating a plane closed curve about an axis that is coplanar with and spaced from the curve. Preferably the curve has inner and outer surface generating segments. The inner segment is located closer to the axis than the outer segment. Generally the outer segment may be essentially w-shaped. The member thus has respective inner and outer surface portions which correspond in transverse cross-sectional shape to the shape of such segments of the curve.
In one preferred form of the invention, the inner segment of the curve may also be essentially w-shaped and complementary to said outer segment, whereby the saddle shaped member has a w-shaped transverse cross-sectional configuration. In another preferred form of the invention, the inner segment of the curve may be essentially arcuate and convex relative to the axis, whereby the saddle shaped member has an xcex5-shaped transverse cross-sectional configuration.
In accordance with the principles and concepts of the invention, the saddle shaped member may have a pair of opposed end walls and said outer surface portion may have a plurality of parallel, alternating ridges and grooves that extend between the end walls. In a more particular and specific form of the invention, both of the surface portions may have a plurality of parallel, alternating ridges and grooves that extend between the end walls. In one preferred form of the invention, the end walls may have a w-shaped configuration. In another preferred form of the invention, the end walls may have an xcex5-shaped configuration.
In one preferred form of the invention, the saddle shaped member may have a plurality of holes that pass through the ridges and grooves in a generally radial direction relative to said axis. In addition, the saddle shaped member may be provided with a plurality of notches formed in the ridges, which notches extend in a direction generally parallel to the axis. Preferably the element may be formed of a ceramic material.
In accordance with the concepts and principles of the invention, a method of constructing a packed bed for a mass transfer tower is provided. The method may comprise the steps of providing a plurality of packing elements as described above and installing the same on a support tray of the mass transfer tower. The invention also provides a method of constructing a packed bed for use as a heat sink. In accordance with this aspect of the invention, the method may comprise the steps of providing a plurality of packing elements as described above and installing the same on a support tray of a heat sink vessel. Preferably, in either case, the packing elements may be installed in a random orientation relative to one another.
The invention also provides a method for mass transfer comprising passing mass transfer fluids through a mass transfer tower packed with the improved elements of the invention. Furthermore, the invention may also provide a method for transferring heat from one fluid to another fluid comprising passing a relatively warmer fluid through a bed packed with the elements of the invention and subsequently passing a relatively cooler fluid through the same bed.